1. Field of the Invention
This invention relates to surgical stapling apparatus, and more specifically to a drive member within a surgical stapler for driving a surgical staple into body tissue.
2. Description of the Prior Art
Surgical stapling apparatus are widely used in surgical procedures to fasten body tissue quickly and efficiently by drivings fasteners, or staples into the tissue. In certain types of staplers, such as those for mechanically stitching together hollow organs, the main linear drive, a cam member, moves transversely to the direction the staples are to be driven. Typically such staplers employ a number of staple drive members or pusher elements located in grooved slots of a staple retaining cartridge and arranged end to end in rows. Under normal operation the transversely moving cam contacts a cam surface on the drive member thereby pushing the staple driver down the grooved slot. The drive member transmits linear motion from the driving cam to the staples. The rows of staples are thereby driven into the body tissue to be fastened.
An example of such a drive member is illustrated in Green et al. U.S. Pat. No. 3,490,675. The drive member disclosed therein has a pusher plate, guide rails, and a V-shaped portion for contacting the driving cam.
A further modification is illustrated in Green U.S. Pat. No. 3,499,591, which discloses a two staple driver. It is more advantageous to be able to drive double rows of staples with a single cam stroke instead of single rows since a double row of staples will have greater holding strength. The two staple driver disclosed therein is an integral piece construction comprising two drive sections in separate planes, with a V-shaped top surface for contacting the pusher cam. Each staple pair is staggered longitudinally (i.e., each staple is positioned diagonally behind the other, in a zig-zag fashion) and bridges the push-bar path.
When the Green '591 double pusher ejects two staples to engage tissue, the forces generated tend to be balanced in both the side-to-side and front-to-back directions, thereby decreasing the offset loadings on the pushers and reducing their tendency to bind. The tips of the pusher bars in Green '591 used to move the pusher and eject staples are arranged, relative to the pushers, so that the maximum force that must be exerted during the formation of staples into a B-shape occurs at only one staple pair at a time. This is accomplished by staggering the tips of the pusher bars in the longitudinal direction.
Strekopytov 3,252,643 describes a C-clamp instrument that is really two instruments side-by-side. The replaceable magazine has two rows of staples separated from a third row. The instrument is fired once to apply two rows of staples, the tissue is then manipulated, and the instrument is fired again to apply the third row of staples.
As is apparent from the prior art, several issues arise in designing drive members for driving a plurality of surgical staples. In particular, failure to effectively balance the forces applied to the drive member when ejecting staples may result in a tendency for the staple pusher to bind against the walls of the pusher slot and to jam. Moreover, drive members for driving a plurality of staples tend to offer more resistance to longitudinal movement of the drive cam and they therefore require that the surgeon apply a greater force to operate the stapler. It is desirable that the drive member permit application of a relatively smooth ejection force throughout the operation.